The present invention relates to the art of a corrosion-resistant metal material such as a coated metal, which corrosion-resistant coated metal can be used in a wide variety of applications such as, for example, used for architectural materials, gasoline tanks, automotive products, appliances, etc.; however, the invention has broader applications and relates to various coating alloy compositions based primarily upon tin and several novel methods and processes used therein such as plating and/or heating (i.e flow heating, hot dip coating, metal spraying), pretreatment of the metal material prior to coating, applying an intermediate metal layer prior to coating, controlling coating thickness, and post-treating the coated metal material (i.e. weather treating, oxidizing coating, passivating intermetallic layer, rolling or cutting processed material).
Over the years, architectural materials, such as metal roofing systems and metal siding systems, made of pliable metals in various sheet gauge thicknesses have been used. Metals such as carbon steel, stainless steel, copper and aluminum are the most popular types of metal used for such architectural materials.
Architectural metal materials made of carbon steel were commonly treated with corrosion-resistant coatings to prevent rapid oxidation of the metal surface, thereby extending the life of the materials. A popular corrosion-resistant coating for carbon steel is a terne coating. Terne coating of stainless steel and copper is also produce, but is much less prevalent than carbon steel due to the natural corrosion-resistant properties of stainless steel and copper. Terne coating has been the predominate and the most popular coating for carbon steel materials due to its relatively low cost, ease of application, excellent corrosion-resistant properties and desirable colorization during weathering.
Terne or terne alloy is a term commonly used to describe an alloy containing about 80% lead and the remainder tin. The terne alloy is conventionally applied to the metals by a hot dip process wherein the base metal is immersed into a molten bath of terne metal by a continuous or batch process. Although terne coated metals have excellent corrosion-resistant properties and have been used in various applications, terne coated materials have recently been questioned due to environmental concerns. Terne coated metals contain a very high percentage of lead. Although the lead in terne alloys is stabilized, there is concern about leaching of the lead from the terne alloy. Environmental and public safety laws have been proposed and/or passed in various communities prohibiting or penalizing the user of materials containing lead. Another disadvantage of terne coated materials is the softness of the terne layer. As noted, terne coated metal sheets are commonly formed into varying shapes. The machines that bend the metal sheets periodically damage the terne coating during bending process. The terne coating is susceptible to damage due to the abrasive nature of the forming machines. The terne alloy has a further disadvantage in that the newly applied terne is very shiny and highly reflective. As a result, the highly reflective coating cannot be used on buildings or roofing systems such as at airports and military establishments. The terne coating eventually loses its highly reflective properties as the components within the terne coating are reduced (weathered); however, the desired amount of reduction takes approximately 1-1/2 to 2 years when the terne coating is exposed to the atmosphere, thus requiring the terne metals to be stored over long periods of time prior to being used in these special areas. The storage time is significantly prolonged when the terne coated materials are stored in rolls and the rolls are protected from the atmosphere.
Tin coating of carbon steel and stainless steel for architectural materials is disclosed in U.S. Pat. No. 5,314,758. Tin coating of copper for architectural materials is disclosed in 5,354,624. The most popular process for applying a tin coating to these metals is by an electroplating process. In an electroplating process, the coating thickness is very thin and typically ranges between 0.3 microns to 30 microns (1.2.times.10.sup.-5 to 1.2.times.10.sup.-3 in.). Such process typically resulted in thin tin layer having a network of small pinholes making the strip generally unacceptable for corrosion-resistant uses. Such electroplated strip may include a base flash layer and/or a cover coating to overcome the pinhole problems inherent with an electroplating process. The tin plated layer is also susceptible to flaking or being scrapped off when the plated strip is drawn and formed into various components. The pinholes and/or flaking off or scraping off of the tin coating is very problematic since tin is not electroprotective under oxidizing conditions. Consequently, discontinuities in the tin coating result in the corrosion of the exposed metal. Tin coatings have the further disadvantage of having a highly-reflective surface. As a result, materials coated with a tin coating cannot be used in an environment where highly-reflective materials are undesirable until the coated materials are further treated (i.e. paint) or the tin is allowed time to oxidize.
Coating base metals with zinc metal, commonly known as galvanization, is another popular metal treatment to inhibit corrosion. Zinc is a relatively low cost material, which is easy to apply (i.e. hot-dip application) and has excellent corrosion resistance. Zinc is also electroprotective under oxidizing conditions to prevent the exposed metal, due to discontinuities in the zinc coating, from rapidly corroding.
However, zinc coatings have several disadvantages that make it undesirable for many types of applications. Although zinc coatings will bond to many types of metals, the bond is not strong and results in the zinc coating flaking off. Zinc also does not form a uniform and/or thick coating in a hot-dip and spray metal process. As a result, discontinuities of the coating are usually found when coating by these processes. Zinc is also a very rigid and brittle metal and tends to crack and/or flake off when the zinc coated materials are formed, i.e. press fitted and/or drawn. When zinc oxidizes, the zinc coating forms a white powdery texture (zinc oxide) which color is unacceptable in many applications.
The use of copper base metals for architectural matters and the like present unique challenges. Copper is typically more corrosion resistant than carbon steel in many environments. However, when copper oxidizes, the oxide forms a green or blue-green layer. This color change is unacceptable in a variety of applications. As disclosed in U.S. Pat. No. 5,354,624, copper base materials can be coated with a tin alloy to form a corrosion resistant material that is pliable and that does not form a green or blue-green layer during oxidation. Although the coating of a tin alloy on copper base materials overcame many of the problems associated with copper materials, the addition of the tin alloy reduces the pliability of the coated copper and forms a highly reflective coating that requires further treating for use in various applications.
Due to the various environmental concerns and problems associated with corrosion-resistant coatings applied to copper materials and the problems associated with the forming of the coated copper material into various types of components, there has been a demand for a copper material that is corrosion-resistant, is environmentally friendly, resists damage during forming, is very pliable, does not oxidize to produce an undesirable color, and is not highly reflective.